The present invention refers to a filtering method for filtering liquids, especially beverages, and a filter device for carrying out this method with the features according to the generic clauses of claim 1.
Such a filtering method is known in practice. It is especially used for sterile filtration in the beverage industry. When beer is being filtered, yeast cells and bacteria can be held back without preventing fine substances, which are responsible for the taste, from flowing through. Such a filtering method and such a filter device are known e.g. from EP-A-368 076.
In the case of this method, the filters are produced in a station outside of the filtering station. Subsequently, one filter at a time is inserted between two filter holders provided in the filtering station. The filter bowls with the filters are stacked up in the filtering station. This method is disadvantageous insofar as the filters have to have a high inherent stability so as to permit the transport of the filters into the filter bowls. For this purpose, a binding agent is admixed to the filter raw material. In view of the fact that such a binding agent contains sugar, its use has the disadvantage that sugar may penetrate into the liquid to be filtered. This can be prevented to a large extent by flushing the filtering station with water prior to starting the filtering process so as to dissolve the binding agent out of the filters. This may, however, have the effect that the height of the filters shrinks by approx. 1/3 at the most. This shrinkage will cause sealing problems in the filter device, and these sealing problems can only be solved by the use of special sealing means for sealing the filters in the filtering station. This makes the device complicated and expensive.
DE-A-39 00 934 discloses a filter device into which filters, which are produced without any binding agent, are inserted. The filters are produced in the filtering station itself by precoating with filter aids. The filter aid is, prior to starting the filtration process, supplied via a common supply line for precoating onto the individual filter holders, which are arranged one on top of the other in a towerlike configuration, so that the individual filters will be formed on said filter holders. When the filtering process has been finished, the filters will be washed out of the device by means of an appropriate rinsing agent.
This method is disadvantageous insofar as the structural design of the filter device is big and complicated because the filter aid is supplied via a common line for producing all filters in common. Hence, the supply line provided must have a sufficiently large diameter. Moreover, it is impossible to check the formation of the individual filters and their uniformity independently and exactly and to change it, if necessary. The fact that the filter aid is supplied via a common line and distributed over all filter carriers may result in an non-uniform formation of the filters. In view of the fact that the filters are not pressed, such non-uniformity will not be levelled out.
With respect to this prior art, it is the object of the present invention to provide an improved and simultaneously simplified filtering method and filter device for filtering liquids without exerting any negative influence on the quality of the filtrate.
In accordance with the present invention, this object is achieved by a filtering method having the features of claim 1.
In view of the fact that each filter is produced by precoating the filter aid onto a filter carrier in a precoating station, i.e. it is produced outside of the filtering station, the production of each individual filter can be supervised and controlled individually. This will guarantee the uniformity of the filters. The fact that production of the filters takes place in a precoating station also permits a simple structural design of the filter station, since it is not necessary to provide there any additional big channel for supplying the filter aid. It follows that it will suffice when the filter device is constructed such that it is suitable for carrying out the filtering process, and, consequently, it can be provided with the optimum structural design. The precoating method for producing individual filters outside of the filtering station can be used for producing simple filters as well as multi-layer filters, which have an asymmetrical structural design, in a reliable and controllable manner. For the purpose of supervision, a visual examination unit can be provided. When the precoating process has been finished, the filter can remain on the filter carrier in the precoating station so that it will dry.
In view of the fact that the filter carrier is introduced into the filtering station together with the filter produced thereon, the filter need not have any inherent stability for transporting the filter into a filter device. Hence, it is not necessary to use in the filter production process any binding agent whose sugar content has a disadvantageous influence on the taste of the filtrate. Furthermore, the above-mentioned problems, which arise with regard to the sealing means when the height of the filters shrinks due to the washing out of the binding agent, are eliminated, since the use of sealing rings becomes completely superfluous because the filter aid is directly precoated onto the filter carriers whereby the filter and the filter carriers will sealingly be connected to one another. In view of the fact that the individual filter carriers plus the filters located thereon are stacked directly one on top of the other in the filter device, each of the filter carriers placed on top of a filter carrier plus filter, which has already been introduced in the filtering station, will fully seal the lower filter when the filter plus filter carriers are pressed together. Depending on the filter material used, the pressing together can be limited by the filter carrier, when the filter material is particularly soft, or by the filter material itself in cases in which a strong filter material is used. Since no unhomogeneousness occurs, the pressing together will take place uniformly. The filter material will be fixed by the pressure applied.
Since the filter need not have any inherent stability for the purpose of transport, the filters produced can have a larger diameter than those produced by prior art methods. This will be advantageous when, for reason of space, the structural dimensions of the filter device should be not so high but comparatively broad.
In view of the fact that, after the end of the filtering process, the filter carriers plus the filters are removed from the filtering station one after the other, whereupon the filters are detached from the filter carriers in a disposal station for the purpose of disposal, the device can also be cleaned in a simple manner. It will just be necessary to remove the filter from each individual filter carrier. There is no necessity of providing cleaning possibilities in the filtering station itself. Nor does the filter device comprise any additional loose parts which would have to be cleaned individually as well. The filters can be separated from the respective filter carrier by knocking, pushing or shaking and disposed of in a disposal station. The disposal station need not necessarily be provided in the same place as the filter device. It may also be provided for several users, e.g. manufacturers of the filter carriers.
In accordance with an advantageous further development of the present invention, a discharge opening of the precoating line is arranged in the precoating station above the filter carrier. It will be advantageous when the discharge opening is located on the centre line through the filter carrier. This will guarantee uniform precoating of the filter aid onto the filter carrier. The uniform distribution of the filter material can be improved by arranging, above the filter carrier and below the discharge opening of the precoating line, a distributor element for distributing the filter aid on the filter carrier. An upwardly curved element, e.g. a convex metal sheet, can be used as a distributor element. The distributor element may also comprise a screenlike plate on which the material supplied for precoating spreads and is then uniformly transferred to the filter carrier via the holes in the plate.
In accordance with a further advantageous embodiment of the present invention, the precoating line is provided with discharge openings, which are arranged radially above an edge of the filter carrier. It will be advantageous to provide these discharge openings with radially arranged nozzles. Furthermore, it may be advantageous to provide the discharge openings with nozzles in such a way that the nozzles have an angle of inclination of from 20.degree. to 70.degree. relative to the radius. The filter aid is then blown with pressure onto the filter carrier, whereby the filter aid will uniformly be distributed on the filter carrier and a sealing contact will be established between the filter aid and the filter carrier. An even better uniformity of the filter material on the filter can be achieved when part of the nozzles defines said angle of inclination with the radius in the direction in which the hands of a clock rotate, whereas another part of the nozzles defines said angle of inclination with the radius in a direction opposite to that in which the hands of a clock rotate. The differently orientated nozzles can be arranged alternately one behind the other. It is also possible to arrange two differently orientated nozzles at approximately the same location one on top of the other, or to provide them as an integral component at a discharge opening.
The filter aid may consist of kieselguhr. Moreover, it may contain water so as to facilitate precoating. Furthermore, it may advantageous when the filter aid contains pearlite or fibres of plastic material or cellulose. The percentage of such fibres may typically be 5 to 20% of the filter aid material.
It can also be advantageous when the precoating station has arranged therein a pressure-exerting device for pressing the filter aid precoated on the filter carrier. By means of the pressing, an even more uniform production of the filter can be guaranteed.
Furthermore, it may be adavantageous when a plurality of precoating stations is provided, since this will speed up the production and the renewal of the filters. It will then also be possible to provide only one precoating line with several discharge openings in the respective precoating stations. It will also be advantageous when several filtering stations are provided. Part of the filtering stations can then, for example, be equipped with new filters while the filtering process is being carried out in the other filtering stations. Simultaneously, filters can be produced in the various precoating stations, said filters being supplied to the non-active filtering stations for replacing there the used filters.
It will also be advantageous when the filters are constructed as metal bowls. The filters can be produced uniformly on such metal bowls. The metal bowls have a long service life and they are easy to clean. Furthermore, the good thermal conductivity of these filter carriers guarantees fast heating of the filtering station, which is necessary for the purpose of sterilization before the filtering process is started.
The filter carriers may have a flat base. Furthermore, the base of the filter carriers may comprise a layer of a porous fabric. This fabric will retain the solid components in the filter and permit the filtrate to pass. It may also be advantageous to use at least one additional layer which consists of a porous fabric and whose pore size differs from that of the first layer. It may also be convenient when the filter carrier is provided with at least one sieve plate including longitudinal slots. In this respect, it will be particularly advantageous when the longitudinal slots have a width of from 0.01 to 0.5 mm. Such longitudinal slots can be formed in said plate either by means of a laser or by means of etching.
Moreover, it may be convenient when the filter carrier is provided with a bottom wall resembling a groove field. This bottom wall can be constructed such that the groove field forms discharge channels below the filter and below the porous fabrics. This will be advantageous in cases in which the filtering process is to be carried out from the top to the bottom and in which the filtrate should, consequently, be discharged below the filter. The groove field may, however, also be arranged in such a way that it forms channels above the filter and above the porous fabrics placed on top of the filter. This will be advantageous in cases in which the filtering process is to be carried out from the bottom to the top and in which the filtrate should, consequently, be discharged above the filter.
In accordance with an advantageous further development of the present invention, there is provided a filter carrier supply means, which supplies the individual filter carriers one after the other to the precoating station. The production of the filters can thus take place more rapidly and more simply, since it can be carried out automatically to a large extent.
Furthermore, it will be advantageous when a transport means is provided, which is used for removing the filter carrier with the filter located thereon from the precoating station as well as for transporting it to and inserting it into the filtering station. It will be convenient when the the transport means comprises a crane and a guide rail. The filter carrier coming from the precoating station can thus directly be installed in the filtering station simply and without difficulty. If the crane additionally comprises a control means with the aid of which the transfer of the filter carrier with the filter from the precoating station to the filtering station is effected automatically, the production of the filters up to the point where they are introduced in the filtering station can be carried out automatically, without any additional work on the part of an operator.
It may also be advantageous when the crane includes a protection box which is adapted to be closed and in which the filter carrier with the filter is enclosed while being transported from the precoating station to the filtering station. It can thus be avoided that the filters are exposed to the polluted atmospheric air during transport. This will increase the durability of the filters.
In accordance with an advantageous further development of the present invention, the filter carriers with the filters can be arranged one on top of the other in the filtering station in such a way that the filter carriers and the filters are axially symmetric with respect to an axis extending at right angles to the horizontal plane. This will be of advantage in cases in which filter carriers with a conical base are used, if said base is constructed with such an angle that oxygen, which is contained in the liquid to be filtered, can pass upwards and, consequently, escape from the device.
In accordance with an additional advantageous embodiment of the present invention, the filter carriers with the filters may be arranged one on top of the other in the filtering station in such a way that the filter carriers and the filter axes are symmetric with respect to an axis which is inclined relative to the horizontal plane. This will be convenient when filter carriers with a flat bottom are used, since the oxygen from the liquid to be filtered can then escape due to the angle of inclination of the bottom surface resulting from said inclination. It will be convenient when said axis is inclined by 30.degree. relative to the plane. It may also be advantageous when the filtering station is adapted to be pivoted in such a way that the axis of symmetry which extends through the filter carriers and the filters can be varied. This permits the filter carriers plus the filters to be stacked up like a tower along the vertical axis of symmetry. When the filter carriers plus the filters have been stacked up like a tower and pressed together, the whole filtering station can be pivoted such that the desired angle of inclination will be obtained. It will then also be possible to correct this angle of inclination, if necessary.
It may just as well be advantageous to arrange the layers of fabric consisting of a porous material between the filters and the respective neighbouring filter carriers. This will have the effect that the layers of fabric need not be secured directly to the filter carriers and that hey can be varied, if necessary.
Furthermore, it may be advantageous when the filtering station has provided therein a backwashing means. With the aid of the backwashing, intermediate cleaning of the filters is effected, whereby the service life of the filters in the filtering station can be extended. It may also be convenient to provide in the filtering station a plurality of flexible hose lines for discharging the filtrate, since the discharge of the filtrate and the filtering process will then take place in a particularly uniform manner.
In accordance with an additional advantageous further development of the present invention, a lifting means can be provided for removing the filter carrier plus the filter associated therewith and for transporting them to the emptying station. This lifting means may comprise a lifting crane. Also the removal of the filter carriers plus the filters as well as the removal of the filters from the filter carriers will thus take place automatically. The filters can be removed by pressing or knocking by means of a slidable element or by a shaking movement. If the disposal container is movable, the used filter material can be removed directly from the emptying station.
According to an additional advantageous further development of the present invention, a cleaning station may be provided in which the filter carriers are cleaned after removal of the filters in the emptying station. The cleaning can be effected e.g. by compressed air or superheated steam. It will also be advantageous when a cleaning transport means is provided, the filter carriers being, after removal of the filters, transferred to said cleaning transport means so that they can be transported through the cleaning system. If the filter carrier supply means additionally extends from the cleaning station to the precoating station, it will be possible to resupply the filter carriers directly to the precoating station after having removed therefrom the filter material and after having them sent through the cleaning station; in said precoating station, the next precoating process can then be started, if necessary.
It will also be of advantage when a superior control electronics and a data processing unit are provided, since the whole filtering process, which comprises the steps of supplying the filter carriers to the precoating station, precoating the filter aid onto the filter carriers, installing the filters with the filter carriers in the filtering station, starting the filtering process, removing the filter carriers and the filters, cleaning the filter carriers and resupplying them to the precoating station, can then be carried out fully automatically.